<?php 
/****************************************************************************
* Software: FPDF_Protection                                                 *
* Version:  1.02                                                            *
* Date:     2005/05/08                                                      *
* Author:   Klemen VODOPIVEC                                                *
* License:  Freeware                                                        *
*                                                                           *
* You may use and modify this software as you wish as stated in original    *
* FPDF package.                                                             *
*                                                                           *
* Thanks: Cpdf (http://www.ros.co.nz/pdf) was my working sample of how to   *
* implement protection in pdf.                                              *
****************************************************************************/

require(dirname(__FILE__).'/fpdf.php');

class FPDF_Protection extends FPDF
{
	var $encrypted;          //whether document is protected
	var $Uvalue;             //U entry in pdf document
	var $Ovalue;             //O entry in pdf document
	var $Pvalue;             //P entry in pdf document
	var $enc_obj_id;         //encryption object id
	var $last_rc4_key;       //last RC4 key encrypted (cached for optimisation)
	var $last_rc4_key_c;     //last RC4 computed key

	function FPDF_Protection($orientation='P',$unit='mm',$format='A4')
	{
		parent::FPDF($orientation,$unit,$format);

		$this->encrypted=false;
		$this->last_rc4_key='';
		$this->padding="\x28\xBF\x4E\x5E\x4E\x75\x8A\x41\x64\x00\x4E\x56\xFF\xFA\x01\x08".
						"\x2E\x2E\x00\xB6\xD0\x68\x3E\x80\x2F\x0C\xA9\xFE\x64\x53\x69\x7A";
	}

	/**
	* Function to set permissions as well as user and owner passwords
	*
	* - permissions is an array with VALUES taken from the following list:
	*   copy, print, modify, annot-forms
	*   If a value is present it means that the permission is granted
	* - If a user password is set, user will be prompted before document is opened
	* - If an owner password is set, document can be opened in privilege mode with no
	*   restriction if that password is entered
	*/
	function SetProtection($permissions=array(),$user_pass='',$owner_pass=null)
	{
		$options = array('print' => 4, 'modify' => 8, 'copy' => 16, 'annot-forms' => 32 );
		$protection = 192;
		foreach($permissions as $permission){
			if (!isset($options[$permission]))
				$this->Error('Incorrect permission: '.$permission);
			$protection += $options[$permission];
		}
		if ($owner_pass === null)
			$owner_pass = uniqid(rand());
		$this->encrypted = true;
		$this->_generateencryptionkey($user_pass, $owner_pass, $protection);
	}

/****************************************************************************
*                                                                           *
*                              Private methods                              *
*                                                                           *
****************************************************************************/

	function _putstream($s)
	{
		if ($this->encrypted) {
			$s = $this->_RC4($this->_objectkey($this->n), $s);
		}
		parent::_putstream($s);
	}

	function _textstring($s)
	{
		if ($this->encrypted) {
			$s = $this->_RC4($this->_objectkey($this->n), $s);
		}
		return parent::_textstring($s);
	}

	/**
	* Compute key depending on object number WHERE the encrypted data is stored
	*/
	function _objectkey($n)
	{
		return substr($this->_md5_16($this->encryption_key.pack('VXxx',$n)),0,10);
	}

	/**
	* Escape special characters
	*/
	function _escape($s)
	{
		$s=str_replace('\\','\\\\',$s);
		$s=str_replace(')','\\)',$s);
		$s=str_replace('(','\\(',$s);
		$s=str_replace("\r",'\\r',$s);
		return $s;
	}

	function _putresources()
	{
		parent::_putresources();
		if ($this->encrypted) {
			$this->_newobj();
			$this->enc_obj_id = $this->n;
			$this->_out('<<');
			$this->_putencryption();
			$this->_out('>>');
			$this->_out('endobj');
		}
	}

	function _putencryption()
	{
		$this->_out('/Filter /Standard');
		$this->_out('/V 1');
		$this->_out('/R 2');
		$this->_out('/O ('.$this->_escape($this->Ovalue).')');
		$this->_out('/U ('.$this->_escape($this->Uvalue).')');
		$this->_out('/P '.$this->Pvalue);
	}

	function _puttrailer()
	{
		parent::_puttrailer();
		if ($this->encrypted) {
			$this->_out('/Encrypt '.$this->enc_obj_id.' 0 R');
			$this->_out('/ID [()()]');
		}
	}

	/**
	* RC4 is the standard encryption algorithm used in PDF format
	*/
	function _RC4($key, $text)
	{
		if ($this->last_rc4_key != $key) {
			$k = str_repeat($key, 256/strlen($key)+1);
			$rc4 = range(0,255);
			$j = 0;
			for ($i=0; $i<256; $i++){
				$t = $rc4[$i];
				$j = ($j + $t + ord($k{$i})) % 256;
				$rc4[$i] = $rc4[$j];
				$rc4[$j] = $t;
			}
			$this->last_rc4_key = $key;
			$this->last_rc4_key_c = $rc4;
		} else {
			$rc4 = $this->last_rc4_key_c;
		}

		$len = strlen($text);
		$a = 0;
		$b = 0;
		$out = '';
		for ($i=0; $i<$len; $i++){
			$a = ($a+1)%256;
			$t= $rc4[$a];
			$b = ($b+$t)%256;
			$rc4[$a] = $rc4[$b];
			$rc4[$b] = $t;
			$k = $rc4[($rc4[$a]+$rc4[$b])%256];
			$out.=chr(ord($text{$i}) ^ $k);
		}

		return $out;
	}

	/**
	* Get MD5 as binary string
	*/
	function _md5_16($string)
	{
		return pack('H*',md5($string));
	}

	/**
	* Compute O value
	*/
	function _Ovalue($user_pass, $owner_pass)
	{
		$tmp = $this->_md5_16($owner_pass);
		$owner_RC4_key = substr($tmp,0,5);
		return $this->_RC4($owner_RC4_key, $user_pass);
	}

	/**
	* Compute U value
	*/
	function _Uvalue()
	{
		return $this->_RC4($this->encryption_key, $this->padding);
	}

	/**
	* Compute encryption key
	*/
	function _generateencryptionkey($user_pass, $owner_pass, $protection)
	{
		// Pad passwords
		$user_pass = substr($user_pass.$this->padding,0,32);
		$owner_pass = substr($owner_pass.$this->padding,0,32);
		// Compute O value
		$this->Ovalue = $this->_Ovalue($user_pass,$owner_pass);
		// Compute encyption key
		$tmp = $this->_md5_16($user_pass.$this->Ovalue.chr($protection)."\xFF\xFF\xFF");
		$this->encryption_key = substr($tmp,0,5);
		// Compute U value
		$this->Uvalue = $this->_Uvalue();
		// Compute P value
		$this->Pvalue = -(($protection^255)+1);
	}
}

?>
